The present invention relates to compounds which can be used to selectively deliver moieties to nerve cells. More specifically, the invention relates to compounds which include a therapeutic moiety and facilitate absorption of the therapeutic moiety by nerve cells.
Our understanding of the structure and function of the nervous system has been greatly advanced owing to enormous progresses made in field of neuroscience. Cellular and molecular mechanisms of neuron growth and development and diseases associated with the central and peripheral nervous systems are studied extensively by using rapidly growing techniques in molecular and cell biology. However, a need still exists for efficacious treatments of many neurological disorders including Alzheimer""s disease, Parkinson""s disease, Huntington""s disease, schizophrenia, severe pain, multiple sclerosis, bipolar disease, and diseases of the nervous system due to infection by viruses and other microorganisms (herpes simplex, HIV, cytomegalovirus, parasites, fungi, prion, etc.).
Many neuropharmaceutical agents have been developed to treat diseases of the nervous system, but their usefulness has been hampered by severe side effects partially due to nonspecific interactions between these agents and cells or tissues other than the targeted cells. For example, steroid hormone cortisone and its derivatives are widely used to treat inflammation in the body including the nerve system to reduce symptoms such as swelling, tenderness and pain. However, the steroid dosage has to be kept at the lowest effective level because of its severe side effects. Steroid hormone binds to its cognate nuclear hormone receptor and induces a cascade of cellular effects, including programmed cell death of the neurons in the brain (Kawata M., et al., J. Steroid Biochem. Mol. Biol. 65: 273-280 (1998)). Since steroid hormone receptors, such as glucocorticord receptor for cortisone, distribute in a wide variety of tissues and cells, nonspecific interactions of the hormone with its cognate receptor in different sites is unavoidable if the drug is circulated systemically.
A need continues to exist for an effective system for delivering therapeutic agents selectively to nerve cells and nerve tissues. Various techniques have been developed to deliver drugs, but with only limited success. For example, liposomes have been used as carrier molecules to deliver a broad spectrum of agents including small molecules, DNAs, RNAs, and proteins. Liposome mediated delivery of pharmaceutical agents has major drawbacks because of its lack of target specificity. Attempts have been made to overcome this problem by covalently attaching whole site-specific antibody or Fab fragments to liposomes containing a pharmaceutical agent (Martin et al., Biochem. 20, 4229-4238, (1981)). However, an intrinsic problem of particular importance in any liposome carrier system is that in most cases the targeted liposome does not selectively reach its target site in vivo. Whether or not liposomes are coated with antibody molecules, liposomes are readily phagocytosed by macrophages and removed from circulation before reaching their target sites.
Compounds of the present invention include compounds having the general formula:
Bxe2x80x94Lxe2x80x94M
where:
B is a binding agent capable of selectively binding to a nerve cell surface receptor and mediating absorption of the compound by the nerve cell;
M is a moiety which performs a useful non-cytotoxic function when absorbed by a nerve cell; and
L is a linker coupling B to M.
In one embodiment, the compounds have the general formula:
Bxe2x80x94Lxe2x80x94TM
where:
B is a binding agent capable of selectively binding to a nerve cell surface receptor and mediating absorption of the compound by the nerve cell;
TM is a therapeutic moiety which has a non-cytotoxic therapeutic effect when absorbed by a nerve cell; and
L is a linker coupling B to TM.
In another embodiment, the compounds have the general formula:
Bxe2x80x94Lxe2x80x94IM
where:
B is a binding agent capable of selectively binding to a nerve cell surface receptor and mediating absorption of the compound by the nerve cell;
IM is a non-cytotoxic imaging moiety which can be used to image a nerve cell or an intracellular component of the nerve cell; and
L is a linker coupling B to IM.
In regard to each of the above embodiments, particular classes of binding agents B which may be used include, but are not limited to, nucleic acid sequences, peptides, peptidomimetics, antibodies and antibody fragments. Examples of nucleic acids that can serve as the binding agent B include, but are not limited to, DNA and RNA ligands that function as antagonists of nerve growth factors or inhibit binding of other growth factors to nerve cell surface receptors. Examples of peptides that can serve as the binding agent B include, but are not limited to, members of the nerve growth factors (neurotrophin) family such as NGF, BDNF, NT-3, NT-4, NT-6; derivatives, analogs, and fragments of nerve growth factors such as recombinant molecules of NGF and BDNF; and synthetic peptides that bind to nerve cell surface receptors and have agonist or antagonist activities of nerve growth factors.
Antibodies, derivatives of antibodies and antibody fragments can also serve as the binding agent B. Examples of this type of binding agent B include, but are not limited to, anti-human trka monoclonal antibody 5C3 and anti-human p75 monoclonal antibody MC192.
The therapeutic moiety TM is selected to perform a non-cytotoxic therapeutic function within nerve cells. Examples of non-cytotoxic functions which the therapeutic moiety TM may perform include, but are not limited to, the functions performed by adrenergic agents, analgesics, anti-trauma agents, anti-viral agents, gene therapy agents, and hormones (growth factors, interferons, etc.). Examples of classes of therapeutic moieties include, but are not limited to, adrenergic agents (e.g., epinephrine, norepinephrine, dopamine, etenolol), analgesics (e.g., opioids, codeine, oxycodone), anti-trauma agents, anti-viral agents (e.g., acyclovir, gancyclovir, AZT, ddI, ddC, etc.), gene therapy agents (e.g., DNAs or RNAs which introduce a gene or replace a mutated gene), steroids (e.g., cortisone, progesterone, estrogen), and hormones (e.g., growth factors, interferons).
The imaging moiety IM is a non-cytotoxic agent which can be used to locate and optionally visualize a nerve cell or an internal component of the nerve cell which has absorbed the imaging moiety. Fluorescent dyes may be used as an imaging moiety IM. Radioactive agents which are non-cytotoxic may also be an imaging moiety IM.
In general, the linker may be any moiety which can be used to link the binding agent B to the moiety M. In one particular embodiment, the linker is a cleavable linker. The use of a cleavable linker enables the moiety M linked to the binding agent B to be released from the compound once absorbed by the nerve cell. The cleavable linker may be cleaved by a chemical agent, enzymatically, due to a pH change, or by being exposed to energy. Examples of forms of energy which may be used include light, microwave, ultrasound, and radiofrequency.
The present invention also relates to a method for selectively delivering a moiety into nerve cells comprising the steps of:
delivering to a patient a compound having the general formula:
Bxe2x80x94Lxe2x80x94M
xe2x80x83where:
B is a binding agent capable of selectively binding to a nerve cell surface receptor and mediating absorption of the compound by the nerve cell;
M is a moiety which performs a useful non-cytotoxic function when absorbed by a nerve cell; and
L is a linker coupling B to M.
having the compound selectively bind to a nerve cell surface receptor via the binding agent B; and
having the compound be absorbed by the nerve cell mediated by the binding of the binding agent B to the nerve cell surface receptor.
In one embodiment, moiety M is a therapeutic moiety TM as described herein and in another embodiment is an imaging moiety IM.
The above method can be used to deliver therapeutic moieties for treating a variety of neurological disorders when the therapeutic moiety TM is a moiety useful for treating such neurological disorders.
The above method can be used to deliver therapeutic moieties for treating pain when a therapeutic moiety TM for treating pain, such as an analgesic, is included as the therapeutic moiety TM in the compound.
The above method can also be used to deliver steroid hormones for treating nerve damage when a therapeutic moiety TM for treating nerve damage, such as a steroid hormone, is included as the therapeutic moiety TM in the compound.
The above method can also be used to stimulate nerve growth when a therapeutic moiety TM for inducing the production of a nerve growth factor is included as the therapeutic moiety TM in the compound.
The above method can also be used to treat infected nerve cells infected with viruses or immunize nerve cells from viruses when the therapeutic moiety TM in the compound is an antiviral agent.
The above method can also be used to perform gene thereapy when the therapeutic moiety TM is a gene therapy agent.